At the Rotterdam Dokhaven WWTP the first full-scale application of the SHARON process has been constructed. In the SHARON process, rejection water from dewatering of digested sludge is treated for N-removal. It concerns a highly active process operating without sludge retention. The single tank reactor is intermittently aerated. Due to differences in growth rate nitrite oxidisers are washed out of the system while ammonia oxidisers can be maintained, resulting in N-removal over nitrite. The SHARON process has been selected after comparison with several other techniques. The feed of the SHARON tank is concentrated, with ammonia concentrations over 1 g N/l. The first results show that conversion rates of 90% are quite possible with N-removal mainly via the nitrite route. The process was shown to be stable. Due to the high inlet concentrations pH control is of great importance, preventing process inhibitions. The acidifying effect of nitrification can be compensated completely by CO2 stripping during aeration and by denitrification. Heat production by biological conversions appeared to be significant, due to the high inlet concentrations, and contributes to the optimal operating temperature of 30-40°C.